Does 2g 3g 4g matter with Wi-Fi? Iphone?

I'm on tmobile and if i get an iphone it will be 2g and thats slow, but if i just use Wi-Fi will it will it still be slow on my Wi-Fi? Or does it matter?

If you are in Wi-Fi it will run however fast your Wi-Fi is. Now your call quality won't be too good and you won't receive texts as fast

If your Wi-Fi is good, the phone will be as fast as that, because most all phones will use Wi-Fi over cellular network. If you are out of the Wi-Fi zone, it will just use the cellular network. Wi-Fi or not, call quality and placement speed as well as sending and receiving texts won't be as fast as 3g or 4g, because calls and sms take place over the network, not Wi-Fi (depending on the phone and/or carrier)